Multilayer ceramic chip capacitors are generally manufactured by alternately applying an internal electrode-forming paste and a dielectric paste in layers by conventional green sheet, printing and other methods and simultaneously firing the resulting layers as an integral stack. Palladium (Pd) and palladium alloys have been widely used as the internal electrodes although relatively inexpensive nickel (Ni) and nickel alloys are now used as a substitute for expensive palladium.
Undesirably, internal electrodes of Ni or Ni alloy are oxidized if fired in the ambient air. To prevent oxidation, the stack after binder removal is fired under an oxygen partial pressure lower than the equilibrium oxygen partial pressure of Ni and NiO. The dielectric layer is oxidized again by a further heat treatment. In this case, SiO.sub.2 is added as a mineralizer for densification of the dielectric material while Al.sub.2 O.sub.3 is often added incidentally. The grain boundary phase components including BaO and TiO.sub.2 as well as these components are sources for a loss of insulation resistance upon firing in a reducing atmosphere.
Mn addition and Ca substitution are useful measures for preventing a loss of insulation resistance due to reduction of the dielectric layer.
However, multilayer chip capacitors having internal electrodes of Ni or Ni alloy have an extremely short life of insulation resistance and are less reliable as compared with multilayer chip capacitors having internal electrodes of Pd fired in the atmospheric air.